Extended Vocabulary auger excavator foundation gears jib shaft trenches Vocabulary effort fulcrum inclined plane lever load pulley screw wedge wheel and axle Picture Credits Every effort
Trang 1Scott Foresman Science 4.16
Nonfi ction Summarize • Captions
• Labels
• Text Boxes
• Glossary
Simple Machines
ISBN 0-328-13906-8
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Scott Foresman Science 4.16
Nonfi ction Summarize • Captions
• Labels
• Text Boxes
• Glossary
Simple Machines
ISBN 0-328-13906-8
ì<(sk$m)=bdjage< +^-Ä-U-Ä-U
Trang 21 How does an excavator use a simple
machine to do work?
2 Why do mobile cranes need special legs?
3 What work does a bulldozer do, and what
simple machine does it use?
4 Many complex
machines are made from simple machines
Write to explain how simple machines can
be put together to make complex machines Use details from the book to support your answer
5 Summarize Write a summary
explaining the stages of constructing
a new building
What did you learn?
Extended Vocabulary
auger excavator foundation gears
jib shaft trenches
Vocabulary
effort
fulcrum
inclined plane
lever
load
pulley
screw
wedge
wheel and axle
Picture Credits
Every effort has been made to secure permission and provide appropriate credit for photographic material
The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.
Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).
Opener: Albert Normandin/Masterfi le Corporation; 4 Albert Normandin/Masterfi le Corporation;
8 Leslie Garland Picture Library/Alamy Images; 11 (BR) Niall MacLeod/Corbis; 13 (B) Getty Images.
Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson
ISBN: 0-328-13906-8
Copyright © Pearson Education, Inc All Rights Reserved Printed in the United States of America
This publication is protected by Copyright, and permission should be obtained from the publisher prior to any
prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,
mechanical, photocopying, recording, or likewise For information regarding permission(s), write to
Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.
3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05
by Marilyn Greco
Trang 3What You Already Know
In science, work means using force
to push or pull an object or to cause a
change Machines make work easier Some
simple machines help you use less force
Others change the direction of the force
you use Simple machines include the lever,
the wheel and axle, the pulley, the inclined
plane, the wedge, and the screw
The lever is a long bar that rests on
a support called the fulcrum A lever is used
to lift a load The effort is the push or pull
that makes the load move Levers are put into
groups based on where the fulcrum, effort, and
load are
The wheel and axle is a special kind of
lever It turns or moves objects The axle
is a rod that goes through the center of the
wheel The handle of a screwdriver is a wheel
The blade is the axle You use force to turn the handle
A pulley is a wheel with a rope, a wire, or a chain
around it You can pull on the rope or chain to make the
wheel move A pulley can change the direction of force
The screwdriver
is a wheel and axle.
3
A ramp is an example of an inclined plane It helps you apply less force to move an object over
a greater distance
A wedge is similar to two inclined planes put together A force at one end of a wedge moves the other end of the wedge forward
A screw is a kind of inclined plane The slanting ridges that wrap around a screw are called threads
Screws can fasten things, lift things, and hold things together
Simple machines can be put together to make complex machines A can opener is a complex machine It uses a wedge, levers, and wheels and axles
Many complex machines are used for building Let’s see some of the machines we might fi nd on
a construction site
The can opener
is a complex machine.
Trang 4Construction Site
Construction of new buildings is a common sight
People build new malls, apartments, houses, schools,
factories, and skyscrapers There are four stages in the
construction of a new building In the fi rst stage, the
ground is prepared and the foundation is laid Next,
workers build the frame of the building Then the frame
is covered with glass, metal, or wood Finally, the interior
is completed
Very large machines are used mostly in the fi rst stages
of building construction Complex machines such as
bulldozers, excavators, cranes, and cement mixers use
simple machines to do work
On a building site,
machines help
people do work.
5
The Inclined Plane
A ramp is an example
of an inclined plane
Pushing an object up a ramp is easier than lifting
it straight up.
A construction site is a busy place Workers do many different kinds of work, and they use many kinds of machines to help them Heavy equipment and other machines reduce the effort required to turn plans into a fi nished building
Workers who operate heavy equipment must know how their machines work Machine operators understand how the different kinds of simple
machines help them to dig, lift, turn, pour, and haul heavy loads
Perhaps the simplest of the simple machines is the inclined plane It has no moving parts! Other simple machines are a bit more complicated, but they all help us do work with less effort The inclined plane is used in the ramp and in other simple and complex machines Simple machines help get work done at a building site
force
load
Trang 5Digging and Shifting
Before a building can be built, the ground must be
prepared so the foundation can hold the building’s
tremendous weight and keep it stable To make these
preparations, a worker uses an excavator The work of
the excavator is to loosen, scoop, and lift many loads of
dirt The excavator drops the dirt into a dump truck,
which takes it to another site The excavator digs out
trenches, or ditches, that will be used for the building’s
concrete foundation
This excavator uses levers that are joined together to dig and lift dirt.
7
The Lever
A lever is a bar resting
on a fulcrum Force pushing down on one end
of the bar lifts a load at the other end.
On the building site, an excavator digs and lifts using a simple machine The arm of the excavator is
a series of levers Each joint of the arm is a fulcrum
The load at the end of each lever is raised when force
is applied in the opposite direction at the other end
Levers change the direction of force They also allow more work to be done while using less
force The closer the fulcrum is to the load, the less force is required to do the job
load
A wheelbarrow is a complex machine It is a lever The wheel at the front is the fulcrum
The wheel is also a wheel and axle
fulcrum force
Trang 6Drilling
Even before any digging starts, drills are used
to make holes in the ground at a construction site Soil samples are collected for analysis
Engineers use soil analysis to decide the depth and type of foundation that will be needed
Tall buildings require special foundations that will support their weight An auger is a piece of equipment used to drill large holes
in the ground These holes will hold underground columns that help support the buildings Smaller hand drills are used to
fi nish work inside the buildings
Workers use a giant auger to dig holes for underground columns.
9
A drill uses an inclined plane wrapped around
a bar called a shaft The tip of the shaft narrows to
a point Force is applied to push the pointed end
of the drill into the material to be cut The sharp edge cuts a hole in the material The spiral design
of the drill allows this machine to continue cutting deeper and deeper Drills and augers are designed so that they can be
removed from the holes they make
force
The Screw
A screw works much like a drill
The head of the screw has a slot to hold a screwdriver The screwdriver turns the screw around and around
The spiraling threads of the screw are a kind of inclined plane The screw makes
a hole as it pushes deeper and deeper.
Power drills can
be used to make small holes.
motion
Trang 7Pushing and Cutting
The bulldozer uses the same simple machine that
the ramp and the screw use It uses the inclined plane
The blade of the bulldozer is a special type of inclined
plane known as a moving wedge
On the bulldozer, force pushing on the wider end of
the wedge pushes the thinner edge against the ground
This edge can slice into the ground or scrape the surface
A bulldozer can also pick up dirt and rocks The
inclined plane changes some of the forward-moving
force into upward force By using a wedge, the effort
needed to move heavy dirt and rocks is reduced
The blade of
a bulldozer is a
wedge It is used
to cut and push.
11
Wedges can be used on building sites in other ways
One simple wedge is a saw A saw has small grooves on
it that are called teeth If you move a saw back and forth on material such as wood, the teeth cut into the wood and push it apart The saw acts as a wedge by forcing pieces of the wood to separate
A nail is another wedge
It is similar to a screw A hammer pounds the fl at head of the nail into a surface The pointed end of the nail makes
a hole as it is pushed
in deeper
The Wedge
The wedge is a type of inclined plane The wedge shape of an axe blade makes it an excellent tool for splitting wood The blade starts with downward force as it enters the wood This changes to sideways force that splits the wood apart.
The force splits wood.
The blade
is a wedge.
The teeth of a saw are sharp wedges that reduce the effort needed to cut wood.
Trang 8Lifting Heavy Loads
Many buildings are supported by steel beams and
parts made of concrete Such building materials are very
strong, but they are also extremely heavy The machine
most often used to lift heavy materials and place them in
precise locations is the crane
Some cranes can easily move from one location to
another Mobile cranes are those that can move around
They have special legs that extend to keep them steady
while they work These legs also help the crane support
the weight of heavy loads Tower cranes are those that
are used to build skyscrapers They are fi xed
in one place and do not move
Big cranes lift very
heavy materials.
13
A crane is made of many pulleys The pulleys make heavy objects easier to lift A crane lifts objects with
an arm called a jib Because cranes lift extremely heavy objects, balance is very important The jib of a tall crane has many openings that allow wind to pass through it
Without the open frame, a strong wind might push the entire crane over
The Pulley
Pulleys are grooved wheels with a cable running over them
Pulling on one end of the cable raises a load at the other end Pulleys reduce the effort needed
to lift objects
Tower cranes are not mobile
The open frame of the jib keeps the crane steady.
effort pulleys
load
Trang 9Wheels in Action
The wheel and axle is used in many places on
a building site The axle is a shaft that is joined to
a wheel at its center Turning the wheel also turns
the axle
A wheel and axle can lift heavy loads A cable is
used to connect the load to the axle Turning the wheel
requires less force than turning the axle As the wheel
turns, the cable winds around the axle and moves
the load
The wheel and axle can be used to move a vehicle
The engine of a vehicle is powerful enough to move the
axle The moving axle then moves the wheel The larger
rim of the wheel covers a greater distance than the
turning axle Some construction equipment moves on
wheels that are taller than the workers driving them!
effort
The Wheel and Axle
A wheel and axle can be used
to lift heavy objects A load is
attached to the axle by a cable
The load is lifted with less effort
by turning the wheel It takes less
effort to turn the wheel than it
takes to turn the axle.
force
load axle
15
Gears are important parts
of construction machinery and are used for many purposes Gears can make a giant vehicle move faster or slower or change direction
In a cement mixer, gears also direct power from the engine
to turn the mixer full of heavy cement
There is plenty of work
at a building site! Bulldozers, saws, cranes, drills, and
cement mixers all use simple machines to get the job done
The large wheel turns slowly.
Gear teeth
Gears send power from the engine to mix the cement.
Gears
Gears are wheels with teeth that fi t together
Force applied to one wheel moves all of the wheels that are connected
Gears can increase or decrease speed or change the direction of motion.
Trang 10Glossary
auger a large tool for making holes
excavator a large tool that loosens, scoops, and
lifts loads of soil and rock
foundation the part of a building that supports
all the other parts
gears wheels with teeth that fi t into the
teeth of other wheels so that when one wheel turns, so do the others
jib the arm of a crane on which
a load is placed
shaft a bar that supports the turning
parts of a machine
trenches ditches; deep grooves
1 How does an excavator use a simple
machine to do work?
2 Why do mobile cranes need special legs?
3 What work does a bulldozer do, and what
simple machine does it use?
4 Many complex
machines are made from simple machines
Write to explain how simple machines can
be put together to make complex machines Use details from the book to support your answer
5 Summarize Write a summary
explaining the stages of constructing
a new building
What did you learn?
Extended Vocabulary
auger excavator foundation gears
jib shaft trenches
Vocabulary
effort
fulcrum
inclined plane
lever
load
pulley
screw
wedge
wheel and axle
Picture Credits
Every effort has been made to secure permission and provide appropriate credit for photographic material
The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.
Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).
Opener: Albert Normandin/Masterfi le Corporation; 4 Albert Normandin/Masterfi le Corporation;
8 Leslie Garland Picture Library/Alamy Images; 11 (BR) Niall MacLeod/Corbis; 13 (B) Getty Images.
Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson
ISBN: 0-328-13906-8
Copyright © Pearson Education, Inc All Rights Reserved Printed in the United States of America
This publication is protected by Copyright, and permission should be obtained from the publisher prior to any
prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,
mechanical, photocopying, recording, or likewise For information regarding permission(s), write to
Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.
3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05